1. Field of the Invention
This invention relates to fungal endophytes of host plants, such as the grass Elymus canadensis (Canada wild rye—CWR). In particular the invention relates to epichloë endophytes (i.e. Neotyphodium) which do not interfere with flowering by their host plants, and to synthetic combinations of these endophytes with improved strains of a host plant.
2. Description of the Related Art
Elymus canadensis (Canada wild rye—“CWR”) is a native perennial cool season bunch grass, a member of the Triticeae host tribe that is known to harbor clavicipitaceous fungal endophytes (Bultman & White, 1988; White & Bultman, 1987; Schardl & Leuchtmann, 1999; Vinton et al., 2001). It is tolerant to a range of soils, winter hardy, and able to grow across the United Sates and as far north as southern Alaska. Canada wild rye is often used for prairie restoration, conservation and erosion stabilization, and young CWR plant tissue is palatable and nutritious to grazing animals. In particular, CWR has been reported to harbor an ascomycete fungal endophyte, Epichloë elymi. The fungal endophyte systemically colonizes intercellular spaces of leaf blades, leaf sheaths and culms of the host plant, and is typically seed transmissible, although infection of other plant parts may also occur. Endophytic fungi are often considered to be involved in a symbiotic relationship with their host plant, and such fungi have been utilized in grass breeding research programs (Bouton et al., 2002).
Previous studies have indicated that epichloë endophytes identified in Elymus species are Epichloe elymi, which are of sexual origin and have the ability to form stroma and perithecia on the plant culm and interfere with development (“choke”) the developing inflorescence (Bultman & White, 1988; White & Bultman, 1987; Schardl & Leuchtmann, 1999), resulting in reduced growth and reproduction of the host plant. In one study of endophyte-infected CWR prairie grasses, formation of sexual reproductive structures (stroma, perithecia, and/or ascospores) by an endophyte did not occur. However, the endophytes from that study were not subjected to phylogenetic analysis (Vinton et al. 2001). Epichloë and Neotyphodium species and strains are thought to have arisen and co-evolved with host plant species, and hybridization events between endophytes, resulting in formation of new endophytic strains and species, displaying either or both of sexual and asexual reproductive forms, is also thought to have occurred. Hordeum bogdanii was recently shown to contain an endophyte that apparently arose via such a hybridization event (Moon et al., 2004).
Many epichloë endophytes provide bioprotection to their hosts by producing alkaloids and other metabolites that have anti-insect and anti-herbivore properties. More recently, the genes required for the biosynthesis of some of these compounds, known as peramine, lolines, indole-diterpenes and ergot alkaloids have been isolated and sequenced (Damrongkool et al., 2005; Spiering et al., 2005; Tanaka et al., 2005; Wang et al., 2004; Young et al. 2006). E. elymi is known to produce the insect feeding deterrent peramine (Clay & Schardl, 2002; Schardl & Leuchtmann, 1999; Siegel et al., 1990), while Epichloë amarillans, an endophyte of the Aveneae host tribe may also produce alkaloids such as lolines. Thus CWR plants colonized by endophytes, including Epichloë sp. and Neotyphodium strains, may be tested for the presence of fungal metabolites.
U.S. Pat. No. 6,111,170 describes synthetic combinations of endophyte/fescue cultivars. U.S. Patent Publications 20060121593 and 20060150273 relate to grass endophytes, such as Neotyphodium lolii and Neotyphodium coenophialum. 
While it is known in the art that the presence of a fungal endophyte can lead to enhanced vegetative growth of a host plant, the endophyte may reduce the host plant's reproductive fitness by interfering with flower development, or may reduce the agronomic value of a host plant crop by production of toxic metabolites such as alkaloids. Thus, there is a need in the art to improve the agronomic properties of host forage grasses such as E. canadensis, as well as to promote the seed yield of a host plant, by protecting the grass from Epichloë sp. that produce metabolites at levels toxic to herbivores and/or that reproduce sexually.